Tap for pressing elastic thread profiles

ABSTRACT

The tap comprises a groove forming portion (1) with a shank (2) having a thread forming portion (3) such that the thread pitch thereof is equal to that of the groove forming portion (1), the crests of the thread forming portion (3) being axially displaced from those of the groove forming portion (1). The thread forming portion (3) is threadedly positioned behind the groove forming portion (1) for axial movement on the shank (2), the movement thereof being limited by a stop (4) arranged on the shank.

TECHNICAL FIELD

The invention relates to the art of manufacturing products havingelements of helical shape by plastic deformation of the metal of a workpiece and may be utilized for pressing internal threads of an elasticprofile in through and preferably blind holes.

BACKGROUND ART

Known in the art are taps for pressing elastic thread profiles capableof tapping through holes only.

After the thread has been cut the tapped part is screwed off the tap andreleased over the shank of the tap.

Such a tap for pressing elastic thread profiles comprises a grooveforming portion and a thread forming portion arranged on the tap axis inseries and having points and threads of equal pitch. These portions areinterconnected by a neck portion having a length which is less than thatof the thread to be tapped. Also, the crests of the thread formingportion are axially displaced from those of the groove forming portion.

The amount of displacement is that of half the pitch of the thread to betapped.

Motion of the groove forming portion through the hole of a part producesa helical groove either by cutting or pressing. At the moment the threadforming portion comes into operation the groove forming portion acts asa threading block providing a lead to the thread crests of the threadforming portion between the valleys of the helical groove that has beenformed.

The thread forming portion impresses a thread by reshaping the helicalgroove into a confined space, which is arranged in the core of thethread profile that has been formed. The space reduces the sectionalarea of the thread profile formed, which makes it possible to increaseelastic deformation of the profile along the axis of the thread.

This ensures a more favorable load distribution between threads of athreaded connection and improves its strength (SU, Inventor'sCertificate No. 625,824 published Apr. 19, 1977, Int. Cl. B 21 H 3/08,of Dniepropetrovsky ordena Trudovogo Krasnogo Znameni gorny institut im.Artema).

This tap is unsuitable for pressing elastic thread profiles in blindholes because the groove forming portion, as the tap is being backed outof the hole, will distort the thread that has been formed by reason ofthe axial displacement of its crests from those of the thread portion.

DISCLOSURE OF THE INVENTON

The invention has for its object to provide a tap for pressing elasticthread profiles in blind holes, wherein the groove forming portion andthe thread forming portion are so connected that in backing the tap outof the threaded hole the crests of the thread of the groove formingportion are disposed in the roots of the thread profile formed and donot distort the thread.

The object set forth is attained by the provision of a tap for pressingelastic thread profiles, comprising on the shank of a groove formingportion a thread forming portion such that the thread pitch thereof isequal to that of the groove forming portion, the crests of the threadforming portion being axially displaced from those of the groove formingportion, wherein according to the invention the thread forming portionis positioned behind the groove forming portion for axial movement onthe shank, the movement thereof being limited by a stop arranged on theshank.

According to a preferred embodiment of the invention the groove formingportion has flutes such that the cutting edges thereof are adjacent theheels of the sides of the flutes on the back of the groove formingportion.

The tap of the invention provides for pressing elastic thread profilesin blind holes due to the fact that as the tap is backed out of thethreaded hole the groove forming portion does not distort the thread.

Because the groove forming portion moves on the internal thread of thethread forming portion in a similar way as along a threading block, asthe tap is backed out the result is, that the crests of the thread ofthe groove forming portion are disposed in the roots of the threadformed, which makes it possible to simultaneously screw out the twoportions.

By cutting away the remaining helical groove by means of the cuttingedges of the flutes of the groove forming portion, as the tap is backedout, the common force required to back the tap out of the hole isdecreased.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will now be described in detail with reference to theaccompanying drawings, in which:

FIG. 1 is a general view of the tap in the course of pressing thethread;

FIG. 2 is a view of the tap as it is backed out of the threaded hole;

FIG. 3 is a bottom view of the groove forming portion.

An arrow in FIG. 3 shows the direction of thread.

BEST MODE FOR CARRYING OUT THE INVENTION

A tap for pressing elastic thread profiles in blind holes comprises agroove forming portion 1 having a shank 2. Adjacent the groove formingportion on the shank 2 there is a thread for engaging a thread formingportion 3, which is followed by a stop 4 rigidly mounted as by pin orwelding on the shank 2 so as to provide a predetermined axialdisplacement of the tap portions in pressing an elastic thread profileas the stop comes in contact with the thread forming portion 3.

On the faces of the groove forming portion 1 there are cut out flutes 5such that the cutting edges 6 thereof are adjacent the heels of thesides of the flutes on the back of the groove forming portion.

The tap operates as follows.

The groove forming portion 1 forms a helical groove along the length ofthe surface in which the profile of the thread is to be impressed as itmoves in the hole by a self-pulling action.

As the thread forming portion 3 moves axially along shank 2 by the screwaction along the shank thread, it comes in contact with the stop 4whereby the crests of the thread forming portion 3 are received betweenthe valleys of the helical groove formed in the hole in the part. As aresult of the passage of the thread forming portion 3 the metal isdisplaced and the helical groove is reshaped into the thread profilethat has been formed.

As the tap is being backed out of the hole the frictional forces betweenthe profile of the thread produced and the thread forming portion 3 holdthe latter in the hole without any rotation.

As the tap is backed out, the cutting edges 6 of the flutes 5 in thegroove forming portion 1 cut away some turns of the remaining helicalgroove up to the point at which the threads formed by thread formingportion 3 commence.

In doing this, the groove forming portion 1 moves outwardly of the holeand along the internal thread of the thread forming portion 3 until itcomes into contact with the thread forming portion, whereupon bothgroove forming portion 1 and thread forming portion 3 are simultaneouslyunscrewed from the hole in the part. As the tap is backed out the crestsof the groove forming portion are received in the roots of the threadproduced.

INDUSTRIAL APPLICABILITY

Such a tap may be used in any branch of mechanical engineering such asaircraft manufacture, in the automotive and tractor industry, in themachine-tool industry and so on, for producing internal threads ofimproved strength in through and blind holes in parts of ductile steelsand alloys.

We claim:
 1. A tap for pressing elastic thread profiles, comprisingashank including a groove forming portion for forming a helical groove; athread forming portion threadedly carried on said shank and having athread pitch thereof equal to that of the groove forming portion, thecrests of the thread forming portion axially displaced from those of thegroove forming portion; and a stop member positioned on said shank; saidthread forming portion movable axially along said shank between saidstop member and said groove forming portion.
 2. A tap as claimed inclaim 1 wherein said groove forming portion has flutes including cuttingedges and heel portions, said cutting edges positioned adjacent saidheel portions of the flutes and operative only when the tap is backedout of a threaded hole.